As light source technology evolves, light emitting diodes (LEDs) and lasers are being used in ever growing applications. These types of light sources, due to their increased optical efficiency and low power consumption are starting to replace standard light sources such as halogen, florescent, etc.
The problem still keeping LEDs and lasers from becoming key light sources in the illumination/multimedia industry is the inability to provide high optical power with relatively low power consumption, as well as inability to provide small physical size with overall low price of the light source, which is also due to the low efficiency of today's projection system that enforces high power sources.
A laser light source composed of a single laser diode is too expensive for light source applications due to the method of fabrication and the high power out put required.
A Vertical Cavity Surface Emitting Laser (VCSEL) has been developed. VCSEL is a semiconductor microlaser offering significant advantages over edge-emitting lasers (EEL) currently used in the majority of fiber optic communications devices. EELs emit coherent light or infrared energy parallel to the boundaries between semiconductor layers. VCSEL emits its coherent energy perpendicular to the boundaries between the layers. VCSELs have high performance and low cost advantages. The VCSELs based structure can be diced directly from the wafer in two-dimensional array configuration. VCSEL operates with low threshold currents thus enabling high-density arrays. surface-normal emission of VCSEL and nearly identical to the photo detector geometry gives easy alignment and packaging; VCSELs provide circular and low divergence output beams thus eliminating the need for corrective optics. VCSEL has lower temperature-sensitivity compared to edge-emitting laser diodes, and high transmission speed with low power consumption.
A vertical cavity surface emitting laser and a method of fabrication thereof is disclosed for example in U.S. Pat. No. 6,542,531. This electrically pumped VCSEL comprises an active cavity material sandwiched between top and bottom DBR stacks. The top DBR has at least one n-semiconductor layer. The device defines an aperture region between the structured surface of the active cavity material and the n-semiconductor layer of the top DBR stack. The structured surface is formed by a top surface of a mesa that includes at least the upper n++ layer of a p++/n++ tunnel junction and the surface of a p-type layer outside the mesa. The structured surface is fused to the surface of the n-semiconductor layer of the DBR stack due to the deformation of these surfaces, thereby creating an air gap in the vicinity of the mesa between the fused surfaces. The active region is defined by the current aperture which includes the mesa surrounded by the air gap, thereby allowing for restricting an electrical current flow to the active region, while the air gap provides for the lateral variation of the index of refraction in the VCSEL.
U.S. Pat. No. 6,546,029 discloses a micro-electromechanically tunable vertical cavity photonic device and a method of fabrication thereof. A tunable Fabry-Perot vertical cavity photonic device comprises top and bottom semiconductor DBR stacks and a tunable air-gap cavity therebetween. The air-gap cavity is formed within a recess in a spacer above the bottom DBR stack. The top DBR stack is carried by a supporting structure in a region thereof located above a central region of the recess, while a region of the supporting structure above the recess and outside the DBR stack presents a membrane deflectable by the application of a tuning voltage to the device contacts.
Nowadays most of the VCSELs work within the non-visible range, mostly for purposes of telecommunication although some promise has been made in demonstrating visible red VCSELS.
New generation of FP lasers with internal 45 degrees reflecting mirror has also been fabricated to enable the FP laser to be Surface-Emitting.